1. Field of the Invention
The present invention relates to a lithographic apparatus, an illumination system, and a method for providing a projection beam of EUV radiation.
2. Description of Related Art
A lithographic apparatus is a machine that applies a desired pattern onto a target portion of a substrate. Lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that circumstance, a patterning structure, such as a mask, may be used to generate a circuit pattern corresponding to an individual layer of the IC, and this pattern can be imaged onto a target portion (comprising part of one or several dies) on a substrate (e.g., a silicon wafer) that has a layer of radiation-sensitive material (resist). In general, a single substrate will contain a network of adjacent target portions that are successively exposed. Known lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion in one go, and so-called scanners, in which each target portion is irradiated by scanning the pattern through the projection beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction.
Lithographic apparatus include, for example, an illumination system for providing a projection beam of radiation. In an extreme ultra-violet (EUV) system, the illumination system typically includes a radiation-production system for producing extreme ultra-violet radiation (EUV), and a radiation-collection system for collection of the EUV produced by the radiation-production system.
Examples of radiation-production systems includes laser produced plasma sources and discharge plasma sources. A laser produced plasma source usually comprises an object, which may also be a gas, that is hit by a laser. This causes a secondary emission, e.g. EUV light, as well as the production of undesired particles, referred to as particles or debris particles.
During use of an illumination system, the particles that are produced as a by-product of the production of the EUV radiation typically enter the radiation-collection system, which causes pollution, or contamination. If the particles have a high velocity, the particles may cause damage to the radiation-collection system. It is possible that other parts of the illumination system that are “downstream,” with respect to the radiation-collection system, may suffer from the presence and/or impact of these high velocity particles.